Isoetes changleensis Y.C. Chen & X. Liu

Liu, Chenlai, Yu, Xiaolei, Song, Xiaoli, Shao, Jingjing, Chen, Yuchu & Liu, Xing, 2024, Two new diploid species of Isoetes (Isoetaceae: Lycopodiopsida) from Southeastern China based on morphological and molecular evidence, Phytotaxa 642 (1), pp. 37-49 : 41-42

Isoetes changleensis Y.C. Chen & X. Liu , sp. nov. ( Figure 1 )

Diagnosis: — Isoetes changleensis is similar to I. longpingii , but the former is distinguished from I. longpingii by its 3-lobed corms (vs 2-lobed corms), deltoid to subcordate ligule (vs cuniform ligule), tuberculate to rugulate megasprore (vs tuberculate-cristate megasprore), a broad equatorial band with densely rugulate ornamentation (vs not observed), and chromosomes 22 (vs 44).

Type:— CHINA, Zhejiang Province, Hangzhou City, Yuhang District , Jingshan Town , Changle Forest farm, elevation 49–50 m, 30°18′41″ N; 119°51′47″ E, 27 September 2021, X. Liu, WH2021092701 (holotype WH!) .

Description: —Plants aquatic and amphibious, growing in wet swamps. Corm 3-lobed. Roots conspicuous, dichotomously branched. Leaves light green, white at base, 0.9–2.1 mm wide in middle, 9–27 cm long, 7.1–11.1 mm wide at the base, erect to ascending, apex acute to attenuate. Ligule deltoid to subcordate, consisting of a thin membrane, inserted above sporangium, generally not visible in dry material. Labium present, reniform-orbicular. Sporangium 9.0– 12.3 mm long, 4.9–6.3 mm wide, oblong, dark brown, at the base of the leaf, the surface of sporangium white, membranous. Velum absent ( Figure 1G and 1H ). Megaspore 246–314 µm diameter (N = 30 +/- SD 16.4 µm), globose, trilete, white; proximal surface tuberculate; distal surface irregular rugulate; the triradial ridge thicker than equatorial ridge; a broad equatorial band with densely rugulate ornamentation ( Figure 1A–1C ). Microspore 14–20 µm long (N = 30 +/- SD 1.7 µm), monolete, heteropolar grey, ellipsoid; proximal surface blunt-tipped echinate; distal surface echinate ( Figure 1D and 1E ). Chromosomes: 2n = 22 ( Figure 1F ).

Etymology: —The specific epithet refers to the localities, Changle Forest Farm in Zhejiang where the species is naturally growing.

Distribution and Habitat: — Isoetes changleensis is only known from two localities (the northwest and southeast of Changle Forest Farm) ( Figure 6 ). The plants are growing in the wet soil ( Figure 1H ), which is dominated by Taxodium distichum (L.) Rich, and associated with Juncus alatus Franch. & Sav , Pseudognaphalium affine (D. Don) Anderb , Ranunculus japonicus Thunb , etc. People are living in the surrounding area, and free-range poultry is raised. The habitat is therefore severely disturbed ( Figure 1I ).

Additional specimens examined: — CHINA. Zhejiang Province, Hangzhou City, Yuhang District, Jingshan Town , Changle Forest Farm , elevation 79–80 m, 30°18′48″ N; 119°51′32″ E, September 2021, X. Liu, WH2021092701 A (isotype WH!) .

Figures

FIGURE 1. Isoetes changleensis Y.C. Chen & X. Liu. A. Proximal view of megaspore. B. Distal view of megaspore. C. Equatorial view of megaspore. D. Proximal view of microspore. E. Distal view of microspore. F. The mitotic chromosomes of root tip cells. G. Megasporangium. H. Microsporangium. I. Habitat. Scale bars:A–C = 100 μm; D–E = 5 μm; F = 20 μm; G–H = 2 mm.

FIGURE 6. Distribution of Isoetes changleensis (blue) and I. yuhangensis (red) in China.